Activation of stress-response genes by retrograde signaling-mediated destabilization of nuclear importin IMPα-9 and its interactor TPR2.

Stress-induced retrograde signal transmission from the plastids to the nucleus has long puzzled plant biologists. To address this, we performed a suppressor screen of the ceh1 mutant, which contains elevated 2-C-methyl-d-erythritol-2,4-cyclopyrophosphate (MEcPP) levels, and identified the gain-of-function mutant impα-9, which shows reversed dwarfism and suppressed expression of stress-response genes in the ceh1 background despite heightened MEcPP. Subsequent genetic and biochemical analyses established that the accumulation of MEcPP initiates an upsurge in Arabidopsis SKP1-like 1 (ASK1) abundance, a pivotal component in the proteasome degradation pathway. This increase in ASK1 prompts the degradation of IMPα-9. Moreover, we uncovered a protein-protein interaction between IMPα-9 and TPR2, a transcriptional co-suppressor and found that a reduction in IMPα-9 levels coincides with a decrease in TPR2 abundance. Significantly, the interaction between IMPα-9 and TPR2 was disrupted in impα-9 mutants, highlighting the critical role of a single amino acid alteration in maintaining their association. Disruption of their interaction results in the reversal of MEcPP-associated phenotypes. Chromatin immunoprecipitation coupled with sequencing analyses revealed that TPR2 binds globally to stress-response genes and suggested that IMPα-9 associates with the chromatin. They function together to suppress the expression of stress-response genes under normal conditions, but this suppression is alleviated in response to stress through the degradation of the suppressing machinery. The biological relevance of our discoveries was validated under high light stress, marked by MEcPP accumulation, elevated ASK1 levels, IMPα-9 degredation, reduced TPR2 abundance, and subsequent activation of a network of stress-response genes. In summary, our study collectively unveils fresh insights into plant adaptive mechanisms, highlighting intricate interactions among retrograde signaling, the proteasome, and nuclear transport machinery.

ZmPILS6 is an auxin efflux carrier required for maize root morphogenesis.

Plant root systems play a pivotal role in plant physiology and exhibit diverse phenotypic traits. Understanding the genetic mechanisms governing root growth and development in model plants like maize is crucial for enhancing crop resilience to drought and nutrient limitations. This study focused on identifying and characterizing ZmPILS6, an annotated auxin efflux carrier, as a key regulator of various crown root traits in maize. ZmPILS6-modified roots displayed reduced network area and suppressed lateral root formation, which are desirable traits for the "steep, cheap, and deep" ideotype. The research revealed that ZmPILS6 localizes to the endoplasmic reticulum and plays a vital role in controlling the spatial distribution of indole-3-acetic acid (IAA or "auxin") in primary roots. The study also demonstrated that ZmPILS6 can actively efflux IAA when expressed in yeast. Furthermore, the loss of ZmPILS6 resulted in significant proteome remodeling in maize roots, particularly affecting hormone signaling pathways. To identify potential interacting partners of ZmPILS6, a weighted gene coexpression analysis was performed. Altogether, this research contributes to the growing knowledge of essential genetic determinants governing maize root morphogenesis, which is crucial for guiding agricultural improvement strategies.

The impact of glucocorticoids therapy on cutaneous wounds in Kawasaki disease: A meta-analysis of randomized controlled trials.

Kawasaki disease (KD) is one of the most challenging diseases that is defined as an acute vasculitis that affects the coronary arteries primarily in children. It causes complications if left untreated at early stages, ultimately leading to death. Corticosteroids have been recognized to treat and cause great impact on the patients with KD. Glucocorticoid is one of the main corticosteroids that are being used to treat KD and cutaneous wounds. However, ineffectiveness of a few glucocorticoids can limit the efficacy of this treatment. This study particularly aimed to elucidate the impact of glucocorticoids on cutaneous wounds in KD. To perform the meta-analysis, a comprehensive literature survey was conducted to unveil the studies and research conducted on Kawasaki patients that revealed different glucocorticoids in the form of specific interventions influencing KD. The literature was searched using numerous keywords, screened and data was extracted to perform the meta-analysis and then it was conducted using the metabin function of R package meta. A total of 2000 patients from both intervention and control groups were employed to carry out the meta-analysis to analyse and evaluate the impact of glucocorticoids on curing KD and cutaneous wounds in patients. The results disclosed that glucocorticoids along with other steroids, mainly IVIG (intravenous immunoglobulin), was an effective intervention to patients suffering from Kawasaki. The results depicted significant outcomes with the values (risk ratio [RR]: 1.08, 95% confidence interval [CI]: 0.58-2.00, p < 0.01) and enlightened the fact that adopting different glucocorticoids may significantly improve the efficacy of skin lesions along with KD. Hence, interventions of glucocorticoids must be utilized in the clinical practice to reduce the incidence of skin wounds and adverse effects caused due to KD.

Tris(1,3-dichloro-2-propyl) phosphate disrupts cellular metabolism within human embryonic kidney (HEK293) cells.

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is a widely used, additive flame retardant that migrates from end-use products, leading to ubiquitous exposure of humans around the world. However, little is known about whether TDCIPP disrupts the physiology of human embryonic cells. Therefore, the objective of this study was to determine whether TDCIPP alters cell viability, cellular metabolism, cytosine methylation, and reactive oxygen species (ROS) levels within human embryonic kidney (HEK293) cells. Relative to vehicle controls, TDCIPP (0.015-0.1225 µM) resulted in a concentration-dependent increase in cell viability, a finding that was driven by an increase in relative ATP abundance. Interestingly, TDCIPP (0.061-0.98 µM) increased the rate of glycolysis - an adaptive mechanism consistent with the Warburg effect exhibited by tumorigenic cells. Moreover, relative to vehicle-treated cells, TDCIPP (0.245-15.63 µM) exposure for 48 h (but not 24 h) resulted in a significant, concentration-dependent decrease in ROS in situ, and TDCIPP (0.245 µM) exposure significantly increased carnosine within the histidine metabolism pathway. However, TDCIPP did not affect global 5-methylcytosine (5-mC) methylation (0.015-15.63 µM), cell membrane integrity (0.061-0.98 µM), nor the abundance of mitochondria (0.061-1.95 µM). Overall, our findings with TDCIPP point to a novel mechanism of action that may be relevant to human embryonic stem cells.

COG-imposed Golgi functional integrity determines the onset of dark-induced senescence.

Plant survival depends on dynamic stress-response pathways in changing environments. To uncover pathway components, we screened an ethyl methanesulfonate-mutagenized transgenic line containing a stress-inducible luciferase construct and isolated a constitutive expression mutant. The mutant is the result of an amino acid substitution in the seventh subunit of the hetero-octameric conserved oligomeric Golgi (COG) complex of Arabidopsis thaliana. Complementation studies verified the Golgi localization of cog7, and stress tests established accelerated dark-induced carbon deprivation/senescence of the mutant compared with wild-type plants. Multiomics and biochemical analyses revealed accelerated induction of protein ubiquitination and autophagy, and a counterintuitive increased protein N-glycosylation in senescencing cog7 relative to wild-type. A revertant screen using the overexpressor (FOX)-hunting system established partial, but notable rescue of cog7 phenotypes by COG5 overexpression, and conversely premature senescence in reduced COG5 expressing lines. These findings identify COG-imposed Golgi functional integrity as a main player in ensuring cellular survival under energy-limiting conditions.

Evaluation of the electrocardiogram RV5 /V6 criteria in the diagnosis of left ventricular hypertrophy in marathon runners.

To assess the value of electrocardiogram (ECG) RV5/V6 criteria for diagnosing left ventricular hypertrophy (LVH) in marathons. A total of 112 marathon runners who met the requirements for "Class A1" events certified by the Chinese Athletics Association in Changzhou City were selected, and their general clinical information was collected. ECG examinations were performed using a Fukuda FX7402 Cardimax Comprehensive Electrocardiograph Automatic Analyser, whereas routine cardiac ultrasound examinations were performed using a Philips EPIQ 7C echocardiography system. Real-time 3-dimensional echocardiography (RT-3DE) was performed to acquire 3-dimensional images of the left ventricle and to calculate the left ventricular mass index (LVMI). According to the LVMI criteria of the American Society of Echocardiography for the diagnosis of LVH, the participants were divided into an LVMI normal group (n = 96) and an LVH group (n = 16). The correlation between the ECG RV5/V6 criteria and LVH in marathon runners was analysed using multiple linear regression stratified by sex and compared with the Cornell (SV3 + RaVL), modified Cornell (SD + RaVL), Sokolow-Lyon (SV1 + RV5/V6), Peguero-Lo Presti (SD + SV4), SV1, SV3, SV4, and SD criteria. In marathon runners, the ECG parameters SV3 + RaVL, SD + RaVL, SV1 + RV5/V6, SD + SV4, SV3, SD, and RV5/V6 were able to identify LVH (all p < .05). When stratified by sex, linear regression analysis revealed that a significantly higher number of ECG RV5/V6 criteria were evident in the LVH group than in the LVMI normal group (p < .05), both with no adjustment and after initial adjustment (including age and body mass index), as well as after full adjustment (including age, body mass index, interventricular septal thickness, left ventricular end-diastolic diameter, left ventricular posterior wall thickness, and history of hypertension). Additionally, curve fitting showed that the ECG RV5/V6 values increased with increasing LVMI in marathon runners, exhibiting a nearly linear positive correlation. In conclusions, the ECG RV5/V6 criteria were correlated with LVH in marathon runners.

25(OH)Vitamin D and autism spectrum disorder: genetic overlap and causality.

OBJECTIVE: To identify whether there exists a genetic correlation and causal relationship between 25(OH)D and autism spectrum disorder (ASD). METHODS: Based on large-scale genome-wide association studies, a series of genetic approaches were adopted to obtain summary statistics. Using linkage disequilibrium score regression, we assessed the shared polygenic structure between traits and performed pleiotropic analysis under composite null hypothesis (PLACO) to identify pleiotropic loci between complex traits. A bidirectional Mendelian randomization (MR) analysis was applied to investigate whether there is a causal relationship between 25(OH)D and ASD. RESULTS: The linkage disequilibrium score regression (LDSC) showed a negative genetic correlation between 25(OH)D and ASD (rg = - 0.227, P < 0.05), and PLACO analysis identified 20 independent pleiotropic loci matched to 24 pleiotropic genes, of which the function reveals an underlying mechanism on 25(OH)D and ASD. In Mendelian randomization analysis, the inverse variance-weighted (IVW) method with OR = 0.941 (0.796, 1.112) and p < 0.474 did not show a causal relationship between 25(OH)D and ASD, while, in the reverse Mendelian randomization analysis, IVW method showed OR = 1.042 (0.930, 1.169), indicating no causal relationship either. CONCLUSION: This study provides evidence for a shared genetic overlap between 25(OH)D and ASD. Bidirectional MR analysis also did not show a definite causal relationship between 25(OH)D and ASD.

Dosage differences in 12-OXOPHYTODIENOATE REDUCTASE genes modulate wheat root growth.

Wheat, an essential crop for global food security, is well adapted to a wide variety of soils. However, the gene networks shaping different root architectures remain poorly understood. We report here that dosage differences in a cluster of monocot-specific 12-OXOPHYTODIENOATE REDUCTASE genes from subfamily III (OPRIII) modulate key differences in wheat root architecture, which are associated with grain yield under water-limited conditions. Wheat plants with loss-of-function mutations in OPRIII show longer seminal roots, whereas increased OPRIII dosage or transgenic over-expression result in reduced seminal root growth, precocious development of lateral roots and increased jasmonic acid (JA and JA-Ile). Pharmacological inhibition of JA-biosynthesis abolishes root length differences, consistent with a JA-mediated mechanism. Transcriptome analyses of transgenic and wild-type lines show significant enriched JA-biosynthetic and reactive oxygen species (ROS) pathways, which parallel changes in ROS distribution. OPRIII genes provide a useful entry point to engineer root architecture in wheat and other cereals.

Reciprocity between a retrograde signal and a putative metalloprotease reconfigures plastidial metabolic and structural states.

Reconfiguration of the plastidial proteome in response to environmental cues is central to tailoring adaptive responses. To define the underlying mechanisms and consequences of these reconfigurations, we performed a suppressor screen, using a mutant (ceh1) accumulating high levels of a plastidial retrograde signaling metabolite, MEcPP. We isolated a revertant partially suppressing the dwarf stature and high salicylic acid of ceh1 and identified the mutation in a putative plastidial metalloprotease (VIR3). Biochemical analyses showed increased VIR3 levels in ceh1, accompanied by reduced abundance of VIR3-target enzymes, ascorbate peroxidase, and glyceraldehyde 3-phophate dehydrogenase B. These proteomic shifts elicited increased H2O2, salicylic acid, and MEcPP levels, as well as stromule formation. High light recapitulated VIR3-associated reconfiguration of plastidial metabolic and structural states. These results establish a link between a plastidial stress-inducible retrograde signaling metabolite and a putative metalloprotease and reveal how the reciprocity between the two components modulates plastidial metabolic and structural states, shaping adaptive responses.

ORA47 is a transcriptional regulator of a general stress response hub.

Transcriptional regulators of the general stress response (GSR) reprogram the expression of selected genes to transduce informational signals into cellular events, ultimately manifested in a plant's ability to cope with environmental challenges. Identification of the core GSR regulatory proteins will uncover the principal modules and their mode of action in the establishment of adaptive responses. To define the GSR regulatory components, we employed a yeast-one-hybrid assay to identify the protein(s) binding to the previously established functional GSR motif, termed the rapid stress response element (RSRE). This led to the isolation of octadecanoid-responsive AP2/ERF-domain transcription factor 47 (ORA47), a methyl jasmonate inducible protein. Subsequently, ORA47 transcriptional activity was confirmed using the RSRE-driven luciferase (LUC) activity assay performed in the ORA47 loss- and gain-of-function lines introgressed into the 4xRSRE::Luc background. In addition, the prime contribution of CALMODULIN-BINDING TRANSCRIPTIONAL ACTIVATOR3 (CAMTA3) protein in the induction of RSRE was reaffirmed by genetic studies. Moreover, exogenous application of methyl jasmonate led to enhanced levels of ORA47 and CAMTA3 transcripts, as well as the induction of RSRE::LUC activity. Metabolic analyses illustrated the reciprocal functional inputs of ORA47 and CAMTA3 in increasing JA levels. Lastly, transient assays identified JASMONATE ZIM-domain1 (JAZ1) as a repressor of RSRE::LUC activity. Collectively, the present study provides fresh insight into the initial features of the mechanism that transduces informational signals into adaptive responses. This mechanism involves the functional interplay between the JA biosynthesis/signaling cascade and the transcriptional reprogramming that potentiates GSR. Furthermore, these findings offer a window into the role of intraorganellar communication in the establishment of adaptive responses.

A plastidial retrograde signal potentiates biosynthesis of systemic stress response activators.

Plants employ an array of intricate and hierarchical signaling cascades to perceive and transduce informational cues to synchronize and tailor adaptive responses. Systemic stress response (SSR) is a recognized complex signaling and response network quintessential to plant's local and distal responses to environmental triggers; however, the identity of the initiating signals has remained fragmented. Here, we show that both biotic (aphids and viral pathogens) and abiotic (high light and wounding) stresses induce accumulation of the plastidial-retrograde-signaling metabolite methylerythritol cyclodiphosphate (MEcPP), leading to reduction of the phytohormone auxin and the subsequent decreased expression of the phosphatase PP2C.D1. This enables phosphorylation of mitogen-activated protein kinases 3/6 and the consequential induction of the downstream events ultimately, resulting in biosynthesis of the two SSR priming metabolites pipecolic acid and N-hydroxy-pipecolic acid. This work identifies plastids as a major initiation site, and the plastidial retrograde signal MEcPP as an initiator of a multicomponent signaling cascade potentiating the biosynthesis of SSR activators, in response to biotic and abiotic triggers.

DHH1/DDX6-like RNA helicases maintain ephemeral half-lives of stress-response mRNAs.

Gene transcription is counterbalanced by messenger RNA decay processes that regulate transcript quality and quantity. We show here that the evolutionarily conserved DHH1/DDX6-like RNA hellicases of Arabidopsis thaliana control the ephemerality of a subset of cellular mRNAs. These RNA helicases co-localize with key markers of processing bodies and stress granules and contribute to their subcellular dynamics. They function to limit the precocious accumulation and ribosome association of stress-responsive mRNAs involved in auto-immunity and growth inhibition under non-stress conditions. Given the conservation of this RNA helicase subfamily, they may control basal levels of conditionally regulated mRNAs in diverse eukaryotes, accelerating responses without penalty.

Retrograde Induction of phyB Orchestrates Ethylene-Auxin Hierarchy to Regulate Growth.

Exquisitely regulated plastid-to-nucleus communication by retrograde signaling pathways is essential for fine-tuning of responses to the prevailing environmental conditions. The plastidial retrograde signaling metabolite methylerythritol cyclodiphosphate (MEcPP) has emerged as a stress signal transduced into a diverse ensemble of response outputs. Here, we demonstrate enhanced phytochrome B protein abundance in red light-grown MEcPP-accumulating ceh1 mutant Arabidopsis (Arabidopsis thaliana) plants relative to wild-type seedlings. We further establish MEcPP-mediated coordination of phytochrome B with auxin and ethylene signaling pathways and uncover differential hypocotyl growth of red light-grown seedlings in response to these phytohormones. Genetic and pharmacological interference with ethylene and auxin pathways outlines the hierarchy of responses, placing ethylene epistatic to the auxin signaling pathway. Collectively, our findings establish a key role of a plastidial retrograde metabolite in orchestrating the transduction of a repertoire of signaling cascades. This work positions plastids at the zenith of relaying information coordinating external signals and internal regulatory circuitry to secure organismal integrity.

Uncovering the functional residues of Arabidopsis isoprenoid biosynthesis enzyme HDS.

The methylerythritol phosphate (MEP) pathway is responsible for producing isoprenoids, metabolites with essential functions in the bacterial kingdom and plastid-bearing organisms including plants and Apicomplexa. Additionally, the MEP-pathway intermediate methylerythritol cyclodiphosphate (MEcPP) serves as a plastid-to-nucleus retrograde signal. A suppressor screen of the high MEcPP accumulating mutant plant (ceh1) led to the isolation of 3 revertants (designated Rceh1-3) resulting from independent intragenic substitutions of conserved amino acids in the penultimate MEP-pathway enzyme, hydroxymethylbutenyl diphosphate synthase (HDS). The revertants accumulate varying MEcPP levels, lower than that of ceh1, and exhibit partial or full recovery of MEcPP-mediated phenotypes, including stunted growth and induced expression of stress response genes and the corresponding metabolites. Structural modeling of HDS and ligand docking spatially position the substituted residues at the MEcPP binding pocket and cofactor binding domain of the enzyme. Complementation assays confirm the role of these residues in suppressing the ceh1 mutant phenotypes, albeit to different degrees. In vitro enzyme assays of wild type and HDS variants exhibit differential activities and reveal an unanticipated mismatch between enzyme kinetics and the in vivo MEcPP levels in the corresponding Rceh lines. Additional analyses attribute the mismatch, in part, to the abundance of the first and rate-limiting MEP-pathway enzyme, DXS, and further suggest MEcPP as a rheostat for abundance of the upstream enzyme instrumental in fine-tuning of the pathway flux. Collectively, this study identifies critical residues of a key MEP-pathway enzyme, HDS, valuable for synthetic engineering of isoprenoids, and as potential targets for rational design of antiinfective drugs.

Orthogonal regulation of phytochrome B abundance by stress-specific plastidial retrograde signaling metabolite.

Plant survival necessitates constant monitoring of fluctuating light and balancing growth demands with adaptive responses, tasks mediated via interconnected sensing and signaling networks. Photoreceptor phytochrome B (phyB) and plastidial retrograde signaling metabolite methylerythritol cyclodiphosphate (MEcPP) are evolutionarily conserved sensing and signaling components eliciting responses through unknown connection(s). Here, via a suppressor screen, we identify two phyB mutant alleles that revert the dwarf and high salicylic acid phenotypes of the high MEcPP containing mutant ceh1. Biochemical analyses show high phyB protein levels in MEcPP-accumulating plants resulting from reduced expression of phyB antagonists and decreased auxin levels. We show that auxin treatment negatively regulates phyB abundance. Additional studies identify CAMTA3, a MEcPP-activated calcium-dependent transcriptional regulator, as critical for maintaining phyB abundance. These studies provide insights into biological organization fundamentals whereby a signal from a single plastidial metabolite is transduced into an ensemble of regulatory networks controlling the abundance of phyB, positioning plastids at the information apex directing adaptive responses.

Correlation between pre-procedural plaque morphology and patterns of in-stent neointimal hyperplasia at 1-year follow-up in patients treated with new-generation drug-eluting stents: An optical coherence tomography based analysis.

INSTRUCTION: Several factors affect the in-stent intimal healing process after drug-eluting stents (DESs) implantation. We hope to investigate the influence of plaque characteristics on subsequent heterogeneous neointimal hyperplasia (NIH) using optical coherence tomography (OCT). METHODS: The study population consisted 217 patients with single-vessel de novo lesions who underwent both pre-procedural OCT scan and 12-month follow-up OCT examination. NIH is defined as at least five consecutive cross-sectional images with no less than 100µm neointimal thickness. According to OCT follow-up, patients were divided into three groups: neointima-covered group, homogeneous, and heterogeneous NIH group. RESULTS: 102 patients were categorized in neointima-covered group, 91 and 24 patients in homogeneous and heterogeneous group, respectively. Time interval between OCT scans was similar (P = 0.55). No significant differences in the patients' age, gender, comorbidities, laboratory findings, procedural, and lesion-related findings were found among these three groups. Heterogeneous group tended to have more subjects presented as acute coronary syndrome (ACS) (P = 0.04) and mean macrophage grade was higher in this group (P = 0.01). While no statistically significant difference concerning mean intimal thickness (P = 0.21) or neointimal burden (P = 0.73) was found between homogeneous and heterogeneous group. Multivariate logistic regression analysis showed that mean macrophage grade (OR: 2.26, 95%CI: 1.12 to 4.53, P = 0.02) and initial clinical presentation of ACS (OR: 2.81, 95%CI: 1.03 to 7.72, P = 0.04) were significant independent risk factors for heterogeneous NIH. CONCLUSION: Mean macrophage grade measured by OCT as a semi-quantitative morphological risk factor, as well as clinical presentation of ACS, was associated with in-stent neointimal heterogeneity after DES implantation.

Interplay of the two ancient metabolites auxin and MEcPP regulates adaptive growth.

The ancient morphoregulatory hormone auxin dynamically realigns dedicated cellular processes that shape plant growth under prevailing environmental conditions. However, the nature of the stress-responsive signal altering auxin homeostasis remains elusive. Here we establish that the evolutionarily conserved plastidial retrograde signaling metabolite methylerythritol cyclodiphosphate (MEcPP) controls adaptive growth by dual transcriptional and post-translational regulatory inputs that modulate auxin levels and distribution patterns in response to stress. We demonstrate that in vivo accumulation or exogenous application of MEcPP alters the expression of two auxin reporters, DR5:GFP and DII-VENUS, and reduces the abundance of the auxin-efflux carrier PIN-FORMED1 (PIN1) at the plasma membrane. However, pharmacological intervention with clathrin-mediated endocytosis blocks the PIN1 reduction. This study provides insight into the interplay between these two indispensable signaling metabolites by establishing the mode of MEcPP action in altering auxin homeostasis, and as such, positioning plastidial function as the primary driver of adaptive growth.

Apixaban attenuates ischemia-induced myocardial fibrosis by inhibition of Gq/PKC signaling.

It was previously found that patients with symptom of myocardial dysfunction had increased levels of thrombin. Apixaban is one of the novel oral anticoagulant drugs widely used in clinic. As the inhibitor of FXa (prothrombin), it inhibits prothrombin conversion into thrombin leading to thrombin deficiency in vivo. However, the effects of apixaban on myocardial fibrosis were still unclear, and the concomitant molecular mechanisms remain to be investigated. Here, we showed that myocardial fibrosis-bearing mice induced by continuous myocardial ischemia (MI) had higher levels of thrombin. Orally administration of apixaban significantly abrogated fibrosis condition and thrombin levels. In vitro, thrombin induced collagen deposition in primary cardiac fibroblasts in a dose-dependent manner. Mechanistic experiments showed that thrombin induced collagen deposition by activation of the Par-1-coupled Gq/PKC signaling. Genetic ablation of Gq or pharmacological inhibition of PKC effectively blunted thrombin-induced collagen deposition in cardiac fibroblasts. Moreover, administration of PKC inhibitor or Gq antagonist obviously blocked MI-induced myocardial fibrosis in mice. To conclude, apixaban attenuates MI-induced myocardial fibrosis by inhibition of thrombin-dependent Par-1/Gq/PKC signaling axis.

Initiation of ER Body Formation and Indole Glucosinolate Metabolism by the Plastidial Retrograde Signaling Metabolite, MEcPP.

Plants have evolved tightly regulated signaling networks to respond and adapt to environmental perturbations, but the nature of the signaling hub(s) involved have remained an enigma. We have previously established that methylerythritol cyclodiphosphate (MEcPP), a precursor of plastidial isoprenoids and a stress-specific retrograde signaling metabolite, enables cellular readjustments for high-order adaptive functions. Here, we specifically show that MEcPP promotes two Brassicaceae-specific traits, namely endoplasmic reticulum (ER) body formation and induction of indole glucosinolate (IGs) metabolism selectively, via transcriptional regulation of key regulators NAI1 for ER body formation and MYB51/122 for IGs biosynthesis). The specificity of MEcPP is further confirmed by the lack of induction of wound-inducible ER body genes as well as IGs by other altered methylerythritol phosphate pathway enzymes. Genetic analyses revealed MEcPP-mediated COI1-dependent induction of these traits. Moreover, MEcPP signaling integrates the biosynthesis and hydrolysis of IGs through induction of nitrile-specifier protein1 and reduction of the suppressor, ESM1, and production of simple nitriles as the bioactive end product. The findings position the plastidial metabolite, MEcPP, as the initiation hub, transducing signals to adjust the activity of hard-wired gene circuitry to expand phytochemical diversity and alter the associated subcellular structure required for functionality of the secondary metabolites, thereby tailoring plant stress responses.

Plastidial metabolite MEcPP induces a transcriptionally centered stress-response hub via the transcription factor CAMTA3.

The general stress response (GSR) is an evolutionarily conserved rapid and transient transcriptional reprograming of genes central for transducing environmental signals into cellular responses, leading to metabolic and physiological readjustments to cope with prevailing conditions. Defining the regulatory components of the GSR will provide crucial insight into the design principles of early stress-response modules and their role in orchestrating master regulators of adaptive responses. Overaccumulation of methylerythritol cyclodiphosphate (MEcPP), a bifunctional chemical entity serving as both a precursor of isoprenoids produced by the plastidial methylerythritol phosphate (MEP) pathway and a stress-specific retrograde signal, in ceh1 (constitutively expressing hydroperoxide lyase1)-mutant plants leads to large-scale transcriptional alterations. Bioinformatic analyses of microarray data in ceh1 plants established the overrepresentation of a stress-responsive cis element and key GSR marker, the rapid stress response element (RSRE), in the promoters of robustly induced genes. ceh1 plants carrying an established 4×RSRE:Luciferase reporter for monitoring the GSR support constitutive activation of the response in this mutant background. Genetics and pharmacological approaches confirmed the specificity of MEcPP in RSRE induction via the transcription factor CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3), in a calcium-dependent manner. Moreover, CAMTA3-dependent activation of IRE1a (inositol-requiring protein-1) and bZIP60 (basic leucine zipper 60), two RSRE containing unfolded protein-response genes, bridges MEcPP-mediated GSR induction to the potentiation of protein-folding homeostasis in the endoplasmic reticulum. These findings introduce the notion of transcriptional regulation by a key plastidial retrograde signaling metabolite that induces nuclear GSR, thereby offering a window into the role of interorgannellar communication in shaping cellular adaptive responses.